Filling path in pgfplot and pushing into background?

Question

I'm using pgfplots to produce a plot of a closed path in the x-y plane. For reasons that are not important here, I would like to fill the closed path. That works fine, but the axes are then hidden by the filled path. How can I push the filled path into the background or the axes into the foreground? I looked at some other questions here that mention using pgflayers, but I can't find that in either the TikZ or pgfplots manuals.

MWE:

\documentclass[10pt]{article}

\usepackage{tikz}
\usepackage{fancyhdr}
\usepackage{pgfplots}

\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}

\begin{document}
\thispagestyle{empty}

\begin{tikzpicture}
\begin{axis}[
  axis x line=middle,
  axis y line=middle,
  xmin = -2.0, xmax =  2.0,
  ymin = -2.0, ymax =  2.0,
]
\addplot[fill=lightgray,mark=none] coordinates {
  (-1.0, -1.0)
  ( 1.0, -1.0)
  ( 1.0,  1.0)
  (-1.0,  1.0)
  (-1.0, -1.0)
}; 
\end{axis}
\end{tikzpicture}

\end{document}

Answer 1

There's a key for the axis environemnt

axis on top

which gives

\documentclass[10pt]{article}

\usepackage{pgfplots}

\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}

\begin{document}
\thispagestyle{empty}

\begin{tikzpicture}
\begin{axis}[axis on top,
  axis x line=middle,
  axis y line=middle,
  xmin = -2.0, xmax =  2.0,
  ymin = -2.0, ymax =  2.0,
]
\addplot[fill=lightgray,mark=none] coordinates {
  (-1.0, -1.0)
  ( 1.0, -1.0)
  ( 1.0,  1.0)
  (-1.0,  1.0)
  (-1.0, -1.0)
}; 
\end{axis}
\end{tikzpicture}

\end{document}